Selector and automatic tuner for radiocircuits



I Jan: 29, .1929; 1,700,281

E. E. BURNS ET m.

SELECTOR'AND AUTOIATIO TUNER. FOR RADIQQIRQUI'IS Filed m. 21 1925,

I ATTORNEYS Patented Jan. 29, 1929. I

A UNITED STATES 1,700,281 PATENT OFFICE.

ELMEB I. BURNS, or 3mm, AND mmononn comm, or CHICAGO, nztmors.

' SELECTOR AND AUTOMATIC TUNERIOR RADIOCIBGUITS.

Application filed December 21, 1925. Serial No. 78,814.

Our invention relates to improvements in selectors and automatic tuners for radio circuits, and it consists in the combinations, constructions, and arrangements herein de- 5 scribed and claimed.

The phenomenon of resonance is very strikin in circuits of radio-frequency. In order t at the energy of the oscillations flowing in one circuit may be transferred more effectively by electro-magnetic induction, the two circuits must have the same natural frequency of oscillation. If the receiving circuit is set into oscillation and the frequency of the circuit is carefully adjusted by a tuning element, a point will be found where a hot wire ammeter, for example, in the audio-frequency part of the circuit, will give a maximum deflection when the receiving circuit is in resonance with'the frequency:

of-the received wave. At all other points, the. ammeter will show a lower reading. It has.

adjustments only that large values of cur rent can be induced in'the receiving circuit.

From actual test, we have found that the increase in plate current of the first stage of audio at resonance with an incoming wave is approximately one milliampere, while theincrease in plate current of the second stage audio is approximately eight milliamperes.

Local signals were being received at the time this experiment was made.

We make use of this additional surge of plate current at resonance for automatically 40 tuning the receiving circuit with the incoming wave.

I The principal object of our invention. is to provlde an automatic tunin element for tuning a receiving circuit wit the incoming wave, the tuning element being controlledby the surge of plate current at resonance.

-A further object of our invention is to provide a device of the type described which makes use of a novel selector for predetermining the desired signals to be received by the receiving or local circuits.

A further object of our invention is to provide a device of the type described in which the.selector and automatic tuning element may be operated by a distant control.

The drawing shows a receiving circuit with the automatic tuner and the selector connected therewith. v a

We have shown a radio receiving circuit em loying two stages of radid-frequency, a etector stage, and' two stages of audiofrequency. These stages are electrically connected to each other and to the sources of current in the usual maImer. We will first describe the selector. We

have shown the selector as tuning one of the stages of radio-frequency. It is obvious that the selector may be a separa selector with t the radio-frequency circuits.

The selector comprises a ratchet 1 which unit if desired, but, for example, we have connected the e tuning element of one of is operatively connected to the tuning element 2 in the radio-frequency circuit 3. The teeth 4 in the ratchet 1 may be of an size desired such as, for example, a size su ficientto turn the tuning element to change the frequency of the circuit 3, ten kilocycles.

It is obvious that any other amount of turning may be substituted for the amount just set forth.

The ratchet 1 is advanced step by step by means of a pawl 5 and the ratchet 1s held in advanced pawl 6.

net 7, this magnet being energized by a osition by means of a second e pawl 5 is actuated by a magmake-an'd-break device indicate generally at 8. The .make-and-break device, in the resent instance, consists of a metal disc aving insulating portions 9. A springpressed terminal 10 yieldingly engages with the periphery of the disc, and when touching the metal between the insulating portions 9, completes a, circuit from a source of current 11 to the ma net 7. This circuit energizes the magnet moving the awl 5, and advancin the ratchet 1 one toot This of course wi l actuate the tuni element.

The disc 8 may be dispos in a. room'of a hotel, for example, and may have the call letters of the broadcasting stations printed thereon, as at 12. The operator, wishing to tune in the station, merely rotates the disc 8 by means of the knob 13 until the call letters of the desired station are brought into view.

While the disc 8 is being rotated, it will cause the pawl 5 to advance the ratchet land the tuning element 2 to the required position for the clrcuit 3' to receive the signals sent out by the station in question. The ratchet 1, together with the ma net 7 and its assoc ate parts, is disposed a jacent to'the tuning element 2 and is electrically connected by the wires 14 with the malre-and-break device 8. In this way, the receiving set may be disposed any distance away from the make-andnet 22'with a source of current 24 and with and rotating -tion, closes the switch 25. This closes the r'eak device. This permits distant control.

A filament switch 15 is of course provided and may now' be turned on. This switch ma also-be disposed adjacent to the makean -break device 8.

We will now describe theautomatic tuning element. This'element may be separate from the radio circuit, if desired, in the same manner as the selector could be a separate. unit. However, to simplify the showmg, we have made use of another of the radio-frequenc' stages. The tuning element 16 is operative y connected to a motor 17 by means of a belt 18. This showing is dia- I grammatic, and it is to be noted that any actuating means for the tuning element 16 may be substituted for the motor 17 without departing from the spirit and scope of our invention.

The motor is electrically connected with a source of current 19 and with a relay switch 20. The switch 20 is closed by means of a lever 21,the lever 21 inturn being controlled by a magnet 22. Wires 23 cannect the maga control switch 25. The switch 25 is dis ppsecl adjacent to the make-and-break device 8. j

The operator, after closing the switch 15 the dial 8 to the required stacircuit to'the magnet 22, energizin the magnet and'actuatiE the lever 21. T e lever 21 in turn closes e motor control switch 20, this switch being held in closed position by means of a catch 26. The motor 17 will now actuate the tuning element 16 until the tun.

of current of one milliampere flows through V the wires 29. The movement of the lever 31 releases the catch 26, thus allowing the spring 32 to open the switch 20. The motor is stopped and therefore ceases to actuate thetuning element 16. The circuits receiving the incoming signal will therefore be held at resonance with each other and will therefore receive the signals from the station desired. I i

It should be noted that although we have shown a rela for controlling the motor circuit, any ot er means for controlling the motor circuit in a similar manner will answer the purpose. The principal feature is to provide some means actuated by an increase of plate current at the point of resonance for stopping further movement of the tuning element whereby the set is automatically tuned.

The lever 31 also actuates a short circuit plate 33 for cutting 011' the flow of current to the magnet 30 after the magnet has actuated the lever 31. It should be noted that the switch'25 is kept closed just long enough to cause the lever 21 'to close the motor switch 20. A difi'erent'station may be tuned in, if desired, by merely turning the dial 8 and then again closing the switch 25. The same operation will be repeated, as heretofore set forth, the tuning element 16 stopping from further movement when the circuits 3 and 27 are in resonance with each other. In stopping the device, the switch 15 is opened. It

is obvious that the automatic tuning element may be used independently of the selector, inthis case the tuning element tuning the receiving circuit into resonance with the incoming signals. If the tuning element is used alone, or the selector is used alone, either device may be employed in any single control radio circuit.

ioo f When the tuning element and the selector I The short circuit plate 33 is adapted to be moved to short thecircuit by a rod 31' con nected to the lever 31. This movementtakes place when the magnet 30 is' energized. .Of

course the rod 31' is returned to inoperative position when the lever 31 drops back into normal posltlon'for again receiving the lever .20, the next time the lever is actuated. It

wlll now appear that the plate 33 still shorts the circuit and that the rod 31 is spaced from theplate.

III

\Vhen the switch 25 is again closed, it will close the switch 20and will also move an arm 21 and swing the lever 32', this lever moving a pin 33', which in turn slides the plate 33 into the position shown.

We claim:

1. In a radio circuit, an electron tube responsive to rectified modulated waves, a

motor-actuated tuning unit, a selector, a

tuning unit actuated by said selector, and means actuated by a change of plate current of said electron tube at resonance for stopping the motor-actuated tuning unit at the frequency for which the selector tuning unit is set.

2. The combination with a radio circuit of a tuning element for bringing the circuit into resonance with received signals and means actuated by a change in the plate current of an electron tube of the receiving circuit operating near a bend of its plate-current grid-voltage curve to stop the movement of the tuning element at resonance.

3. The combination with a radio circuit of a tuning element for bringing the circuit into resonance with received signals, a motor for actuating said element, a source of ourrent-for said motor, and means actuated by a change in theplate current of an electron tube of the receiving circuit operating near a bend of its plate-current grid-voltage curve curve being determined by the constants of the circuit and the intensity of the received signal.

4. The combination with a radio circuit of a tuning element for bringing the circuit into resonance with recelved slgnals, a motor for actuating said element, a source of current for said motor and means actuated by an increase in the plate current of an electron tube of the receiving circuit operatin near the lower bend of its plate-current gri voltage curve for stopping the movement of said motor when the tuning element is at or near the point of resonance.

5. ,The combination with a radio circuit of a tuning element for bringing the circuit into resonance with received signals and means actuated by a change in the plate current of an audio frequency amplifier tube of the receiving circuit and responsive to modulated waves to stop the movement of the tuning element at a point on the resonance curve determined by the constants of the circuit and the intensity of the received signals.

ELMER E. BURNS. THEODORE COHEN. 

